Chris_c is seriously engaged in this task. He has already had some success and published a list of outstanding SL16.Let's wish him good luck and help him.Looking through my database I have found 10 still lifes from his list:

I pushed an update containing everything in this thread, all of Goldtiger's 14-bit SL reductions and many of Bob's converters. I didn't include any of Bob's converters that reduced the population and I didn't include any that looked inapplicable to 16-bit SL lifes. If this means that I have missed out something important then please point it out.

I pushed an update to my glider_synth repo on github based on Bob's recent 16G collection (and hopefully all of the new syntheses in this thread). It contains 225 improvements including 65 SLs that appear for the first time. Many of the most complicated syntheses look to have come via Mark Niemiec's collection.

There are now 3212 SLs with synthesis, 2933 in less than 16 gliders, 85 in 16 gliders, 74 unknown SLs and 61 hard equivalence classes.

My lists are behind Bob's in 101 cases. It looks like the biggest single reason is that Bob uses many converters that reduce the bit count of the object. Bob hasn't yet posted the syntheses for all of the necessary still lifes of bit count greater than 16 and for me to extend to 17 or 18 bit still lifes using my own system it would probably best to do a rewrite in C. Whether this will actually happen is debatable.

Nevertheless, I hope we can work out most of the other discrepancies starting with the 12-14 bit still lifes listed here.